1. Field of the Invention
The present invention relates to a spindle motor for driving a magnetic disk employed for a hard disk drive device of a computer.
2. Description of the Related Art
In a hard disk drive device, the development of a large capacity hard disk drive device has been recently promoted. In order to meet the demand for such a large capacity in the hard disk drive device, the spindle motor used in the hard disk drive device must rotate at high speed.
As an example of the spindle motor employed for the hard disk drive device, a device shown in FIG. 2 has been known. This spindle motor (spindle motor for driving a magnetic disk) 1 comprises a base member 3 provided with a stator 2 and a hub 5 provided with a magnet 4 opposing to the stator 2. The hub 5 is formed in a substantially tubular shape with a prescribed height so that a magnetic disk (not shown) is fitted to its outer peripheral portion.
The hub 5 comprises a substantially annular hub main body 6 for holding the magnetic disk; a tubular portion with a bottom (hub tubular portion) 7 connected to one end portion (the lower side in FIG. 2) of the hub main body 6; and a tubular hub extended portion 8 extended from the other end portion (the upper side in FIG. 2) of the hub main body 6.
A fixed shaft 10 standing upright on the base member 3 is inserted into a hole (hub hole) 9 formed in the hub main body 6 and the hub extended portion 8. A bearing cartridge assembly 11 is interposed between the fixed shaft 10 and the hub 5. The hub 5 is rotatably supported on the fixed shaft 10 through the bearing cartridge assembly 11.
The bearing cartridge assembly 11 is a bearing (ball bearing) of a type comprising one outer ring 12 and two inner rings (reference numerals are omitted) with a prescribed distance provided therebetween. The end portion of the outer ring 12 in the side of the base member 3 (the lower side in FIG. 2, hereinafter referred to as lower outer ring end portion 12a) protrudes downward from the hub main body 6 in FIG. 2. An end portion in the side opposed to the lower outer ring end portion 12a of the outer ring 12 (the upper side in FIG. 2, hereinafter referred to as upper outer ring end portion 12b) substantially reaches the front end portion of the hub extended portion 8.
In this spindle motor 1, since the widthwise dimension (span) of the outer ring 12 of the bearing cartridge assembly 11 is relatively large, the rigidity of the bearing cartridge assembly (bearing) 11 is high, and accordingly, the unsteadiness of the hub 5 is prevented and running accuracy is high.
In the spindle motor 1, it has been desired to reduce the weight thereof In order to attain the purpose, it may be taken into consideration to reduce the length dimension of the fixed shaft 10 and the widthwise dimension (vertical dimension in FIG. 2) of the bearing cartridge assembly 11 and determine the height of the hub 5 so as to be substantially equal to the height of the end face of the fixed shaft 10 and the end portion of the bearing cartridge assembly 11 whose dimensions are reduced as described above.
However, in the attempt described above, the widthwise dimension (vertical dimension in FIG. 2) of the bearing cartridge assembly 11 is reduced, so that the rigidity of the bearing cartridge assembly 11 is undesirably lowered. Accordingly, the hub 5 is apt to be unsteady upon operation of the spindle motor 1, so that running accuracy may possibly be deteriorated.
The present invention has been made in view of the above circumstances, and an object of the present invention is therefore to provide a spindle motor in which the high rigidity of a bearing can be maintained and the weight can be decreased.
For achieving the object described above, according to one aspect of the present invention, there is provided a spindle motor comprising:
a hub to which a magnetic disk is fitted;
a base member;
a fixed shaft vertically provided on the base member; and
a bearing,
the hub being rotatably supported on the fixed shaft through the bearing, characterized in that
an end portion of an outer ring of the bearing at the front end side of the fixed shaft is set to protrude relative to a bearing holding portion of the hub on which the outer ring of the bearing is held.